IMPACT: International Journal of Research in Applied, Natural and Social Sciences (IMPACT: IJRANSS) ISSN(E): 2321-8851; ISSN(P): 2347-4580 Vol. 2, Issue 8, Aug 2014, 77-86 © Impact Journals
A COMPUTER BASED ANALYTICAL STUDY ON CHELATE COMPOUNDS OF HEAVY METAL IONS INTERACTING WITH AMINO ACID AND NUCLEOBASE K. KUMAR1 & D. K. DWIVEDI2 1
Research Scholar, Department of Chemistry, Pt. S.N.S. Government P.G. College, Shahdol, A. P. S. University Rewa, Madhya Pradesh, India 2
Professor, Department of Chemistry, Pt. S.N.S. Government P.G. College, Shahdol, A. P. S. University Rewa, Madhya Pradesh, India
ABSTRACT The study on mixed - ligand chelation of heavy metal ions Hg (II) and Cd (II) with amino acid taken as primary ligand (A) and nucleobase taken as secondary ligand (B) at silver-silver chloride electrode by the pH - metric technique at 37 ± 1oC in two different molar ratio 1:2:1 and 1:2:2 for mixed- ligand ternary chelates. The stability constants and stability order of MA, MB and MAB complexes have been discussed with the help of SCOGS at fixed temperature and ionic strength. The species distribution curves described the formation of chelate compound play important role in biological system.
KEYWORDS: Chelation, Chelate Compound, pH-Metry, Stability Order, SCOGS, Distribution Curves INTRODUCTION There are a large number of toxic metals are found in nature. They are also known as heavy elements or heavy metals such as arsenic, bismuth, cadmium, chromium lead, manganese, mercury etc. The chelating agent must be of low toxicity and not metabolized so as to persist on changes in the biological system to perform their scavenging functions due to their interaction with metal ions to form metal chelates or dislodging the bound metals and excreting these as soluble chelates from the system. The metal chelates play an important role in biological1analytical2 industrial3, 4, and medicinal5 area. In the present paper amino acid (2-Amino succinic acid) and nucleobase (5-methyluracil) behave as a very good chelating agent which form ternary chelate compound of biological significance interacting with heavy metal ions Hg (II) and Cd (II). Some essential and non - essential or potentially toxic metal ions are present in biological systems6, 7. In biological processes8-10 ternary chelation plays very valuable role. Mercury is a heavy metal may be called the mad hatters mineral. It is a toxic substance which has no known function in human biochemistry or physiology. Cadmium is called the pseudo-macho or the violent element. It is biopersistent and once absorbed by an organism remains resident for many years although it is eventually excreted. The normal and acceptable value of Hg (II) and Cd (II) metals are about 0.25 ppm and 0.08 ppm respectively. Mostly, amino acids are soluble in water which shows zwitter ion in solution. They normally coordinate to metal ions through the amino and carboxylato groups. Attractive ligand-ligand interactions favor the formation of mixed ligand complexes, giving rise to ligand selectivity or a preferred combination of ligands around a metal ion. The importance of metal ion–nucleic acid interactions in the metabolic machinery is well recognized and applied medicinal chemistry. Metal ions can interact with nucleobases and sugar moieties as well as with phosphates. Martin in an extensive review Impact Factor(JCC): 1.4507 - This article can be downloaded from www.impactjournals.us
78
K. Kumar & D. K. Dwivedi
discussed the competition between the N1 and N7 nitrogen atoms in purines for metal ions in aqueous solutions. 2-Aminosuccinic acid play valuable role in absorption of toxins and removal from the bloodstream11, 12 and also acts as a neurotransmitter13. The nucleobase, 5-methyluracil combined with deoxyribose creates the nucleoside deoxythymidine, which is synonymous with the term thymidine. Thymidine is significant because of its involvement in the biosynthesis of DNA and in the preservation and transfer of genetic information.
EXPERIMENTAL Complex formation in solution proceeds by the stepwise addition of the ligands to the metal ion, a number of successive equilibria can be formulated according to Abegg and Bodlander14,15. M+L
ML
ML + L
ML2
MLn-1 + L
MLn
(1)
From Law of Mass Action, [MLn] Kn =
(2) [MLn-1] [L]
Where n represents the coordination number of the metal ions, terms in bracket [ ] refers to the activities of different species and Kn are thermodynamic stepwise stability constant or formation constant. [MLn] βn =
(3) [M] [L] n
Where βn (overall stability constant) is the product of stepwise formation constant. The protonation of the ligand L occurs in steps exactly in the same way as complexation reaction consequently following proton ligand equilibria may be considered: L+H
HL
Hn-1L + H
H nL
(4)
The proton ligand stability constants thus are given by, K nH =
[HnL] (5) [Hn-1L] [H]
Hence βnH, the overall proton ligand stability constant is determined by, βnH =
[HnL] (6) [H]n [Hn-1L]
The formation of mixed - ligand ternary systems can be considered to take place as follows:
Index Copernicus Value: 3.0 - Articles can be sent to editor@impactjournals.us
A Computer Based Analytical Study on Chelate Compounds of Heavy Metal Ions Interacting with Amino Acid and Nucleobase
M + L1 + L2
79
ML1L2 [ML1L2]
β ML1L2=
(7) [M] [L1] [L2]
pH- Metric Titration This paper contains analytical study of mixed - ligand ternary chelates of Hg (II) and Cd (II) with 2-Aminosuccinic acid (A) and 5-methyluracil (B) by potentiometry in aqueous medium using Bjerrum's16 method modified by Irving and Rossotti.17 in two different molar ratio 1:2:1 and 1:2:2. All the solutions were prepared in double distilled water. The pH measurements were done by an electric digital pH meter (Eutech 501) with a glass electrode supplied with the instrument and working on 220V/50 cycles stabilized by A.C. mains. The pH meter has a reproducibility of Âą0.01 pH. The pH meter calibrated with buffer solutions of pH (4.0) and pH (9.2) respectively which were prepared by dissolving buffer tablets (BDH) in double distilled water in appropriate concentrations. A carbonate free sodium hydroxide solution18 was prepared for completion of this work. All the metal salts used were of Analar Grade and were standardized volumetrically by titration with the disodium salt of EDTA 19 is presence of suitable indicators. Each set of solution was then titrated against above carbonate free alkali (NaOH). Following set of solution mixtures were prepared for analytical study: Acid Solution 5 ml NaNO3 (1.0 M) + 5ml HNO3 (0.02M) + 40 ml water Ligand - Solution 5 ml NaNO3 (1.0 M) + 5ml HNO3 (0.02M) + 5ml A (0.01M) + 35 ml. water Binary System (1: 1) (M: A) / (M: B) 5 ml NaNO3 (1.0 M) + 5ml HNO3 (0.02M) + 5ml A (2-ASA) / B (5- MU) (0.01M) + 5 ml M (II) (0.01M) + 30 ml water. Mixed Ligand Ternary System (1:2: 1) (M:A: B) 5 ml NaNO3 (1.0 M) + 5ml HNO3 (0.02M) + 10ml A (2-ASA) (0.01M) + 5 ml Hg (II) / Cd (II) (0.01M) + 5 ml B (5- MU) (0.01M) + 20 ml water Mixed Ligand Ternary System (1:2: 2) (M: A: B) 5 ml NaNO3 (1.0 M) + 5ml HNO3 (0.02M) + 10ml A (2-ASA) (0.01M) +5 ml Hg (II) / Cd (II) (0.01M) + 10 ml B (5- MU) (0.01M) + 15 ml water Calculation of Stability Constant I.G.Sayce20-22 developed a computer program named as SCOGS (Stability constant of generalized species) which employs the conventional non linear least square approach. The program is written in FORTRAN IV. It is capable of calculating simultaneously or individually, association constants for any of the species formed in the system containing up to two metals and two ligands, provided that the degree of complex formation is pH-dependent. Thus, SCOGS may be Index Copernicus Value: 3.0 - Articles can be sent to editor@impactjournals.us
80
K. Kumar & D. K. Dwivedi
utilized to analyse appropriate pH titration data to yield metal-ion hydrolytic constants, stability constants of simple complexes (MA, MB and MA2 etc.). SCOGS may also be used to calculate constants for "mixed" complexes containing two different metals and two different ligands resulting the formation of MAB and M1M2 AB types of complexes.
RESULTS AND DISCUSSIONS The present paper concerned with the formation of metal chelates and evaluation of stability constant of mixed - ligand ternary system in rational study that means single metal and two ligands interacting in different ratios. For the evaluation of overall stability constant (βpqrst) of mixed - ligand ternary complexes of biological significances we apply a special computer programme SCOGS according to which:pM1 /qM2+rA + sB + t(OH)
(M1)p / (M2)q (A)r (B)s (OH)t
[(M1) p / (M2) q (A) r (B) s (OH) t] βpqrst =
(8) [M1] p/ [M2] q [A]r [B]s [OH] t
In above equation the p, q, r and s are either the zero or positive integer and t is a negative integer for a protonated species like H3A, H2A, HA and BH, positive integer for a hydroxo or a deprotonated species like [M (OH)+], [M (OH)2+] and zero for a neutral or normal species like [M A] [M B] and [M A B] etc. Species Distribution Curves The species distribution curves are obtained by plotting percent (%) concentration of the species obtained through SCOGS computer programme against pH. The species distribution curves of studied systems were finally sketched by running the computer program ORIGIN 4.0. Hg (II) - 2-ASA (A)- 5-MU(B) Ternary (1:2:1) System From the species distribution curves given in (figure. 1) it is clear that the binary complex of Hg B exist in good concentration ~ 73% at start of the titration and gradually decreases with increase in pH range. Another binary complex shows its value~ 37% concentration at the pH ~3.3. H2A have the maximum concentration ~ 57% at the start of titration. Ternary complex of Hg AB exist with higher value having maximum concentration ~ 93% at higher pH ~ 9.5.
Figure 1: Species Distribution Curves of 1:2:1 Hg (II)-2-ASA (A) - 5-M U (B) System (1)Hg2+ (2) H3A (3) H2A (4) HA (5) BH (6) Hg(OH)2 (7)Hg A (8)HgB (9) HgAB
Index Copernicus Value: 3.0 - Articles can be sent to editor@impactjournals.us
A Computer Based Analytical Study on Chelate Compounds of Heavy Metal Ions Interacting with Amino Acid and Nucleobase
81
Cd(II)- 2-ASA(A) - 5-MU(B) Ternary (1:2:1) System For this system the distribution curves are represented in figure 2. In the present system H2A species shows maximum concentration ~ 70% at the very initial stage which decreases with the increase in pH range. HA have maximum concentration ~ 90% at the pH ~ 4.8. In this system binary complex of metal and ligand B is existed maximum concentration ~ 96% at the pH range 4.5. Major complex which is ternary complex of Cd AB is attained maximum concentration ~ 98% at the very high pH ~ 9.9.
Figure 2: Distribution Curves of 1:2:1 Cd (II)-2-ASA (A) - 5-MU (B) System (1)Cd2+ (2) H3A (3) H2A (4) HA (5) BH (6)Cd(OH)2 (7) CdB (8) CdAB Hg (II)-2-ASA (A) and 5-M U (B) Ternary (1:2:2) System From the species distribution curves given in (figure 3) it is clear that the binary complex of Hg A exist in concentration ~ 39.5% at pH ~4.2. Another binary complex Hg B shows its maximum concentration ~ 76% at the start of titration. Ternary complex of Hg AB exist with higher value having maximum concentration ~ 90% at higher pH ~ 9.0. Protonated ligand species H3A, H2A, HA and BH shows their remarkable presence. Hydroxo species also existed in this system. H2A attain maximum concentration ~ 57% at the start of titration. HA attain maximum concentration ~ 48% at pH ~ 9.0.The gradual decline in the concentration of binary complexes there is concomitant incline in concentration of ternary complexes species attaining maximum concentration shows the step wise formation of ternary complex.
Figure 3: Distribution Curves of 1:2:2 Hg (II)-2-ASA (A) -5-MU (B) System (1)Hg2+(2) H3A (3) H2A (4) HA (5) BH (6)Hg(OH)2 (7)Hg A (8)HgB (9) HgAB Index Copernicus Value: 3.0 - Articles can be sent to editor@impactjournals.us
82
K. Kumar & D. K. Dwivedi
Cd (II) - 2-ASA (A) and 5-M U (B) Ternary (1:2:2) System The distribution curves for present system represented in (figure 4) in which it is clear that the binary complex Cd B attains maximum concentration ~ 95% at the very initial stage of titration which gradually decreases with the increase in pH range. H2A species shows maximum concentration ~ 72% at the very initial stage which decreases with the increase in pH range. HA species shows maximum concentration ~ 83% at the pH ~ 4.6. Ternary complex of Cd AB attain maximum concentration ~ 98.5% at the very high pH ~ 9.8. Hydroxo species also existed in some extent in this system.
Figure 4: Distribution Curves of 1:2:2 Cd (II)-2-ASA (A) - 5-MU (B) System (1) Cd2+(2) H3A (3) H2A (4) HA (5) BH (6) Cd(OH)2 (7) Cd B (8) Cd AB Overall Stability Constants and Other Related Constants of Binary and Ternary Complexes for M (II) 2-ASA (A) - 5-MU (B) (1:2:1), (1:2:2)) System at 37 ± 10C, I = 0.1 NaNO3. Table 1: Proton-Ligand Formation Constant (Log β00r0t/ Log β000st) of 2-ASA-5-MU at 37 ± 10C, I = 0.1 NaNO3 Complex H 3A H 2A HA BH
log β00r0t/ log β000st 15.26 13.33 9.63 9.94
Table 2: Hydrolytic Constants (Log βp000t/ Log β0q00t) M2+ (aq.) Ions Complex M(OH)+ M(OH)2
Hg -3.84 -6.38
Cd -6.89 -14.35
Table 3: Metal-Ligand Constants (Log βp0r00/ Log β0qr00/ Log βpo0s0/ Log β0q0s0) Binary System Complex MA MB
Hg 13.09 13.45
Cd 4.39 11.33
Table 4: Metal-Ligand Constants (Log βp0rs0/ Log β0qrs0/): Ternary System (1:2:1) Complex MAB
Hg 21.45
Cd 16.54
Index Copernicus Value: 3.0 - Articles can be sent to editor@impactjournals.us
83
A Computer Based Analytical Study on Chelate Compounds of Heavy Metal Ions Interacting with Amino Acid and Nucleobase
Table 5: Metal-Ligand Constants (Log βp0rs0/ Log β0qrs0/): Ternary System (1:2:2) Complex MAB
Hg 21.85
Cd 17.00
Proposed Binary and Mixed – Ligand Ternary Structure of Complexes
Figure 5: M (II)-ASA 4- Coordinated
Figure 6
Figure 7: M (II)-ASA 6- Coordinated
Figure 8: M (II)-ASA-5-MU 4- Coordinated
Index Copernicus Value: 3.0 - Articles can be sent to editor@impactjournals.us
84
K. Kumar & D. K. Dwivedi
Figure 9: M (II)-ASA-5-MU 6- Coordinated
CONCLUSIONS From the above study it is well clear that the amino acid and nucleobase used in this study have strong ability to interact with heavy metal ions and form metal chelates. We know that amino acid shows zwitter ion in solution so they normally coordinate to metal ions through the amino and carboxylato groups. Metal ions can interact with nucleobases and sugar moieties as well as with phosphates. Attractive ligand-ligand interactions favor the formation of mixed - ligand complexes of biological significance having the good ability to removal of heavy metal toxicity. Individual Stability Order •
Mixed ligand ternary (1: 2: 1) System Hg/Cd (II)-2-ASA (A) - 5- MU (B) Hg AB > Cd AB
•
Mixed ligand ternary (1: 2: 2) System: Hg/Cd (II)-2-ASA (A) - 5- MU (B) Hg AB > Cd AB
Overall Stability Order of Investigated Complex Species Hg AB (1: 2: 2) > Hg AB (1: 2: 1) > CD AB (1: 2: 2) > Cd AB (1: 2: 1) > Hg B > Hg A > Cd B > Cd A
REFERENCES 1.
A Sigel and H. Sigel; “Metal ions in Biological System,” Marcel Dekker, New York, 1-44 (1971-2009)
2.
X.J. Yang and C. Pin; Analyst, 3, 453 (2000)
3.
George. St. George, Chem-Chou Chiang and David A. Wilson; Ind.Eng. Chem. Res. 47 (4), 1277 (2008)
4.
Raymond Eller Krik and D. Frederic; ‘Krik-othmer Encyclopedia of Chemical Technology’, John Wiley & Sons Inc., Hooken, Newjersy, 26, 334 (2007)
5.
John R. J. Sorenson; Current medicinal chemistry, 9, 639 (2002)
6.
J.Birch;in Handbook on “Toxicity of inorganic compounds”, Marcel Dekker, New York,383(1988)
7.
A.K.De; ‘Environmental Chemistry’, Third Edition, New Age International Ltd.,Publishers,77(1995)
8.
H. Sigel, Coord.Chem.Rev.,144,287 (1995)
9.
H. Sigel and A. Sigel, (eds), “Metal ions in Biological System,” Dekker, New York 1; 35 (1998)
10. J.P Scharff,in “Metal ions in Biological System”, ed. H. Sigel, Dekker, New York, 2, 2 (1973) 11. F. Khan and P.L. Sahu, Ultra scientist phys, sci., 12, 106 (2008) Index Copernicus Value: 3.0 - Articles can be sent to editor@impactjournals.us
A Computer Based Analytical Study on Chelate Compounds of Heavy Metal Ions Interacting with Amino Acid and Nucleobase
85
12. Colbert, Don, M.D., Toxic Relief, Siloam Publishing, (2003). 13. A ntimo D 窶連niello.Aspartic acid: An endogenous amino acid with animportant neuroendocrine role. Brain Research Reviews 53:215-214(2008) 14. R. Abegg, Z. anorg. Chem. 32, 330 (1904). 15. R. Abegg and G.Bodlander, Z. anorg. Chem. 20, 543 (1899). 16. J. Bjerrum, "Metal Amine Formation in Aqueous Solution". P. Masse &. Sons Copenhagen (1941). 17. H. M. lrving and H.S. Rossitti; J. Chem. Soc. 3397 (1953), 2904 (1954) 18. G. Schwarzenbach and W. Biderman, Helv. Chim. Acta, 31, 331. (1948) 19. F.J. Welcher, The analytical uses of ethylene diamante tetra acetic acid, D.Van Nostarand Company, New York P. 169 (1957). 20. I.G. Sayce, Talanta, 15, 1397, (1968). 21. I.G. Sayce, Talanta, 18, 653, (1970). 22. I.G. Sayce and V.S. Sharma, Talanta, 19, 831, (1972).
Index Copernicus Value: 3.0 - Articles can be sent to editor@impactjournals.us